Cake, chocolate, biscuits, crisps, chips, takeaway and even alcohol are among the inappropriate items served by some owners, the PDSA said.

The charity stressed that many overweight pets develop potentially life-threatening conditions such as heart disease, cancer and diabetes, as well as debilitating conditions including arthritis as a direct result of being overweight.

PDSA has launched its Pet Fit Club competition and has invited owners of overweight and obese pets to take part.

To help fight the flab, it has again launched its Pet Fit Club competition and has invited owners of overweight and obese pets to take part.

"Pet obesity can be tackled, and through a diet and exercise programme like Pet Fit Club we can transform fat pets into fit pets," said PDSA Vet Vicki Larkham-Jones.

"Nearly half of pet owners believe that obesity is the biggest threat to animal welfare in the next 10 years - yet pets continue to be fed unsuitable diets which is fuelling the problem.

"As well as being high in calories, food like takeaways, cake, cheese, chips and crisps are high in fat and sugars which are bad for our pets' waistlines and teeth. Some owners even admitted to giving chocolate and even alcohol, both of which are poisonous to pets and can be fatal."

A woman measuring a dog's belly with tape measure Photo: Alamy

The PDSA highlighted the case study of Lady, the chubby Cavalier King Charles Spaniel from Belfast.

Lady, who is an early entrant to this year's slimming competition, was very thin when rescued by current owner David Palmer last year. But 61-year-old Mr Palmer admitted he had gone too far in his efforts to build her back up to health.

Duke the Labrador before and after last year's PDSA Pet Fit Club Photo: Wales News/PDSA

"We got her just over a year ago from a rescue centre but prior to that she was badly treated on a puppy farm," explained Mr Palmer.

"She was skin and bones and had hardly any teeth left. The only food she seemed to eat was chicken, we also gave her treats and biscuits when she accepted them to increase her weight. But over time she's piled on the pounds. She begs and we find it difficult not to give in to her.

"She's always had breathing problems but this has got worse as her weight has crept up and now she needs an operation. I know that losing weight will also help her in the long term and I want her to be healthy and live a long life."